Bridge Rail and Approach Railing for Low-Volume Roads in Iowa

Bridge rail and approach guardrails provide safety to drivers by shielding more-hazardous objects and redirecting vehicles to the roadway. However, guardrails increase both the initial and maintenance costs of a bridge while adding another object that vehicles may strike. According to current reports, most existing bridges for low-volume roads (LVRs) in the state of Iowa do not have bridge rails that meet current standards. The primary objective of this research was to provide information about bridge rail and approach guardrail on LVRs in Iowa. In support of this objective, statewide descriptive, statistical, and economic crash analyses were performed. The statewide crash analysis found that the overall number of crashes at or on the more than 17,000 inventoried and other noninventoried LVR bridges in Iowa during an 8-year period was fewer than 350, a number that represents less than 0.1% of the statewide reportable crashes. Statistical analysis showed that the frequency of vehicle crashes was higher on bridges with a smaller width in relation to the roadway width. The frequency of crashes appeared to be overrepresented at night or in dark conditions. Systemwide, benefit–cost analyses yielded extremely low benefit–cost ratios for statewide bridge rail improvements. However, specific sites where safety concerns exist should be addressed. Overall, each bridge and its crash history should be evaluated independently to determine beneficial safety impacts.